From buildings, bridges, road and rail to pumped hydro or offshore wind, what you don’t know can bring your project to a grinding halt or make for an unsteady future. Getting a thorough, integrated geotechnical, groundwater and contaminated land site investigation underway as early as possible can help avoid major budget blowouts and project delays – and mitigate the risk of a completed project that cracks, shifts or doesn’t stand the test of time.
We talked with Cristian Loddo, Major Projects Executive, and Mitchell McGinnis, Principal Project Manager, about unravelling the mysteries of what lies beneath.
Nature is complex
Ground and subsurface conditions are notorious for being unpredictable, uncertain and changeable, with significant variation even within short distances.
“One of the forefathers of geotechnical engineering, Karl von Terzaghi, famously said that the products of nature are always complex,” says Cristian. “Because what is under the surface is hidden and uncertain, excavation typically unveils an array of complexities and issues.”
“Substantial unknowns in the subsurface environment can dramatically affect the performance of a project in terms of cost and schedule. We see this regularly during project delivery if the preplanning has been poor or rushed,” he says.
The ground investigation typically includes taking samples for lab testing and conducting downhole testing to gather as clear a picture as possible about material properties, in situ stresses and groundwater conditions – as well as soil, rock and groundwater chemistry. It will also explore the groundwater flow patterns, consider the potential of encountering contamination, and deliver insights into the required design solutions and construction methods to address the anticipated conditions.
“With this information, the design and construction teams can adequately assess the risks and make the design and proposed construction methodology sufficiently robust and resilient to cater not only for the expected conditions, but also for potential variations in these assumptions,” explains Cristian.
Anticipating risk
Risks associated with unforeseen ground conditions are front of mind for many owners and contractors involved in designing and constructing infrastructure projects – and they seem to be arising more frequently.
“One reason why ‘getting out of the ground’ is riskier today than previously, is that many infrastructure projects are being developed in places that are harder to access and develop,” says Mitchell. “This may be because easier locations have already been developed, or because the project may be the last complex piece of a wider solution or a modification or update of existing outdated infrastructure.”
He adds that it has often been wrongly assumed that a contingency might be sufficient to manage ground risk and provide the required level of protection for uncertainties.
“History has shown that it is very difficult to assess and assign an adequate contingency for ground risk without a comprehensive ground investigation having been completed beforehand to identify and describe the expected conditions and how they may vary.” Mitchell explains that this applies to the design of the excavation as well as the methodology that will be used for construction.
“To effectively pre-empt these risks, it is critically important to plan and conduct a phased ground investigation and simultaneously develop a geotechnical ground model,” says Mitchell.
“Developing and updating the ground model as the investigation progresses can help identify and target knowledge gaps, and enable informed engineering decisions to be made before construction begins.”
Starting early and phasing the site investigation to maximise value
It is natural and common for project developers to be eager to get projects underway as quickly as possible. However, it’s certain that taking the time to properly plan, execute and interpret an integrated phased site investigation is a sound investment and could save plenty of lost time due to unanticipated problems later. The investment is also likely to pay ‘dividends’ during project delivery, reducing the risk of unexpected budget overruns.
The following diagram demonstrates how the ability to influence risk and the associated cost both change as the project progresses through planning, design, construction and operation. Clearly, opportunities for intervention diminish and costs rise as the project proceeds through its lifecycle, so it’s best if as much detailed ground investigation can be done as early as possible.
Adapted from Gibson and Hamilton (1994) Analysis of pre-project planning effort and success variables for capital facility projects. Construction Industry Institute Source Document 105.
Mitchell explains that this approach begins in the feasibility stage, with a thorough desktop study followed by initial on-site investigations to document key site characteristics and potential ground-related risks.
“As the project moves from planning into delivery,” he says, “the site investigations should get progressively more detailed, targeting areas of uncertainty or ground complexity. After each investigation stage, the geotechnical ground model, project risk register and proposed risk mitigation strategies should be updated to reflect the new insights that have been gained.” This approach maximises the opportunity to learn from each investigation phase and progressively update the investigation scope.
He says that the documented updates should include how the identified risks will be managed and further mitigated through the adopted design solutions and proposed construction methodology.
“If this step is missed,” he warns, “the potential risk mitigation benefits achievable across the project lifecycle will be forfeited.”
Phased approaches in practice for successful projects
Cristian explains that WSP has successfully implemented a phased approach on many projects. These include the Regional Rail Link, Melbourne Metro, Sydney Metro City and Southwest, Western Harbour Tunnel and Beaches Link and the Suburban Rail Loop.
“Collaborating closely with our clients, we’ve demonstrated the flexibility to proactively and rapidly adapt investigation scopes so that emerging risks are identified and addressed promptly, enhancing the overall success of our projects,” he says.
As well as adopting a phased approach, ground investigation will be further enriched through the cohesive, collaborative and integrated effort of a diverse range of expertise.
Mitchell says, “When projects harness the collective expertise of a range of professionals, the results are a wider range of investigation strategies and approaches, which in turn deliver a more in-depth understanding of expected conditions and the potential ground-related challenges.”
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